1. Field of the Invention
The present invention relates to an inspection system for inspecting a container by obtaining images through radiation, more particularly, to a pulling device for a container inspection system.
2. Description of the Related Art
In the prior arts, the pulling type container inspection system, such as the large scale container inspection system manufactured by Haiman Corporation, Germany and British Airspace Corporation, has been developed in the early years of the nineties of 20th century. The above conventional container inspection system is devised as follows. Stationary accelerator which produces high energy x-ray as radiation source and stationary array detectors which receive x-ray passing through the container are mounted in an inspection passage which is capable of shielding radiation beams. A vehicle carrying the container which is pulled by a special pulling device so as to pass by the inspection passage. When the container passes x-ray, x-ray will transmit through the container and incident on the detectors. As a result, the density distribution of the objects contained in the container is presented in accordance with the variation of the intensity of x-ray. Then, the intensity of x-ray is converted into a corresponding gray degree of an image so that a perspective view of the objects contained in the container can be obtained.
A conventional pulling device is constructed as follows. Specifically, tracks are mounted inside an inspection passage, and a movable pulling vehicle is placed on the tracks. The head of the vehicle carrying the container stops on the pulling vehicle. The pulling vehicle is pulled by a traction system and moved along the tracks so that the vehicle carrying the container is pulled by the pulling device. As such, the vehicle carrying the container passes by the inspection passage.
However, the conventional pulling device of the container inspection system is disadvantageous in the following aspects. Two winding drums, two motors and two inverters are used so as to control the forward and backward movement of the pulling device respectively. Accordingly, the investment of the equipments is increased and the area occupied by the system is enlarged. Further, a traction force is applied to the pulling vehicle by wire ropes which are wound around the two winding drums. With this operation mode, it is difficult to control so as to achieve constant tensile force. Especially at the stage that the pulling vehicle is started or stopped, it may occur that a wire rope on one side is excessively slackened. As a result, the pulling operation can not be carried out stably, thus impeding normal operation of the inspection system.